Efflorescence and Moisture Absorption on Magnesium Oxide Boards in Humid Environments: Causes and Mechanisms​

The core cause of efflorescence and moisture absorption on Magnesium Oxide (MGO) boards in humid environments is the migration and subsequent crystallization of soluble salts from within the board to its surface. Moisture dissolves these salts, facilitating their movement to the surface, where they crystallize into a white, powdery deposit after the water evaporates.

Primary Cause: Migration and Crystallization of Soluble Salts

1.  Introduction of Soluble Salts via Raw Materials

During the production of MGO boards, if the raw materials—particularly the magnesium oxide powder and the magnesium chloride solution (bittern)—are of low purity, they can contain excessive amounts of soluble salts such as sodium chloride, calcium chloride, and magnesium sulfate. These salts remain within the board in ionic form, creating the fundamental condition for potential efflorescence and moisture absorption.

2.  Humid Environment as the Driving Force for Migration

When environmental humidity is high or the board comes into direct contact with water, moisture penetrates the board and dissolves these soluble salts, forming a saline solution. This solution then migrates towards the surface through internal pathways within the board, such as pores and capillaries.

3. Crystallization of Salts due to Water Evaporation

Once the saline solution reaches the surface, the water gradually evaporates due to factors like increased temperature or decreased humidity. The dissolved salts, now lacking a solvent, crystallize and deposit as white crystals on the surface, manifesting as "efflorescence" or "whitening." If the salts do not fully crystallize on the surface, residual saline moisture within the board can cause a persistently damp surface, a phenomenon known as "moisture absorption" or "bittern leakage."

Secondary Contributing Factors: Production Processes, Installation, and Maintenance

1. Deficiencies in Production Processes

Improper production practices increase the risk of efflorescence and moisture absorption. These include incorrect material ratios (e.g., excessive use of magnesium chloride), inadequate mixing, insufficient curing time, or poor control of temperature and humidity during curing. Such deficiencies can result in a less dense internal microstructure with increased porosity and fail to ensure the complete consumption of soluble salts present in the raw materials.

2.Improper Installation and Maintenance

Improper handling during installation and lack of protective maintenance can directly trigger these issues. This includes failure to apply moisture-proof coatings, inadequate sealing of joints, or installation in persistently damp, poorly ventilated, or water-prone areas (e.g., bathroom floors, basement walls). These conditions accelerate water ingress, promoting the dissolution and migration of salts.